Determining Iron Grades of Ores or Concentrates Containing Sulfide Minerals
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IRON ores used in the steel industry must have some certain chemical properties including the amount of Fe(II), Fe(III), and the total Fe. In some geological studies, having an accurate level of Fe(II) and Fe(III) is essential for determining the petrology and mineralogy of an ore.[1] Iron is found naturally in hybrid forms such as oxide, sulfide, carbonate, and silicate. Usually, earth crustal rocks contain some iron in their composition. Iron minerals are abundant in nature and they include magnetite, hematite, siderite, and pyrite.[2,3] Pyrite is the most well-known iron sulfide ore and it occurs in rocks of every geologic age and of virtually every geologic realm.[4] In general, both classical wet methods (e.g., titration) and instrumental methods (e.g., XRF, ICP) are used to determine the amount of chemical elements in a sample. In the wet method, the desired substance is dissolved in suitable acids, which is referred as digestion process. To determine the amount of a chemical element, a certain
MAHDI OSTADRAHIMI, KHODAKARAM GHARIBI, and ALI DEHGHANI are with the Faculty of Mining & Metallurgical Engineering, Yazd University, Yazd, 98195, Iran. SAEED FARROKHPAY is with GeoRessources, University of Lorraine, 54505, Nancy, France. Contact e-mail: [email protected] Manuscript submitted August 12, 2019. Article published online February 18, 2020. METALLURGICAL AND MATERIALS TRANSACTIONS B
volume of the solution (based on the type of elements) is reacted with the corresponding standard reactants and the concentration of each element is obtained from the chemical relationships between the reagent and the reactant. This method of chemical determination is often called ‘titration.’ Usually, this method is used to determine the elements that are present in a high concentration, for example, in the analysis of iron grade of iron ores.[5] In this method, hydrochloric acid is used as the main solvent and the titration is conducted by potassium dichromate (K2Cr2O7). Titration is suitable for measuring the total iron in ores and concentrates containing 30 to 72 wt pct iron.[6] In the instrumental methods, the amount of chemical elements is determined by using a proper instrument. In particular, instrumental methods can be used to determine very low amount of elements. X-ray Fluorescence Spectroscopy (XRF), Atomic Absorption (AA), and Inductively Coupled Plasma (ICP) are among the instrumental methods which are used in mineral industry.[5] It should be highlighted that it is not possible to dissolve sulfide minerals in hydrochloric acid and it is necessary to remove the sulfur bond (i.e., Fe-S) in some other way. For this purpose, nitric acid is often used.[7] While nitric acid is able to dissolve such ores, there is a risk of remaining the acid during the titration process. Also, dissolving the sample with nitric acid, plus neutralization with ammonium hydroxide, is time consuming. Often several hours is required to dissolve the sulfide ore using mixture of nitric, hydrochloric, and
VOLUME 51B, APRIL 202
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